Power distribution boxes, or panel boards, are used to provide electrical power to buildings and other installations. The incoming power lines are routed through the box and more particularly through the circuit breakers housed in the box. The circuit breakers direct the power from the power source to individual circuits inside the building or installation and provide some protection to the circuit by disconnecting the circuit from the power source when the circuit draws more current than it was designed for. In addition to the circuit breakers, the panel board can be expanded to hold other electrical equipment. Panel boards have been extended to house such things as shunt trips, relays, transformer and monitoring equipment.
Surge suppressors have also been added to circuit breakers to provide protection against voltage spikes and surges which are capable of damaging electrical equipment connected to the power distribution box. The surge suppressors protect against these voltage transients by absorbing the excess energy and slowly discharging it to ground. In order for this type of surge suppression to be effective the surge suppression circuitry must be located as close to the circuit breakers as possible because every 12 inches of conductor length between the circuit breakers and the surge suppressors results in 170 volts of let-through voltage, severely compromising the performance and effectiveness of the system.
Previous systems have located surge suppression modules in the panel board itself and wired the modules directly to the busses that distribute the power from incoming lines to circuit breakers. This arrangement provides very good surge suppression performance, but suffers from other drawbacks. The purpose of the surge suppression modules is to keep equipment downline operating without interruptions. However, in a system with surge suppression modules wired, or bolted to the power source, a problem with the module necessitates that power to the panel board and all downline equipment must be disconnected to replace or reset the module, resulting in the very interruption of power the surge suppression was designed to prevent.
To overcome this problem some panel boards have had their surge suppressors wired through one or more of the circuit breakers housed in the panel board. While this approach allows the particular circuit breakers to disconnect the surge suppressor module from the power source and allows the surge suppressor module to be serviced without interrupting power to the other circuit breakers it is an imperfect solution. Circuit breakers in panel boards are nearly always precious commodities, installing surge suppression that would monopolize multiple breakers could often be impractical or impossible.